Rod Selection?

Wheresmywrench?

Wheresmywrench?

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Simply how much larger should the material you select to turn be then the finished part. I'm talking about when you go out and buy a rod for a specific job.Lets say finished size 1/2 inch should it be 1/16" or 1/8" larger in diameter?
 
a lot of times stock is of nominal thickness, that is the material is slightly oversize unless otherwise specified.
2 exceptions i know for sure is in selecting delrin and extruded aluminum, they are right on the money for the size- other materials may have similarities.

if your finished part needs to be .500" and your material is .500" it's possible that no other external machining would be necessary other than possibly knurling or parting.
if you need a finished dimension of .505" you could possibly need to start with 13mm(.511") or larger stock, then turn down to desired diameter.


it really depends on the project and the material used, as to what size selection you'll make
 
Almost as important as getting the right diameter is getting enough length. I always plan on screwing up the first one or two (usually at the very last operation) and having to start over with fresh stock, so I make sure I get enough the first time to do the entire job two or three times.

If by some miracle I luck out and do it right the first time then I have stock on hand for another project somewhere down the line. Maybe someday my odds will improve :)

Stu
 
I'm with Stu, except I worry more about the OD once I get past the surface finish. Extruded stuff like Aluminum or Delrin usually only require a 0.010" reduction in OD to get past the external stuff and get a clean OD to work with. Most tool steels, drill rod and hot rolled material also seem to require less work to prep, while the hot rolled stuff seems to need more. Bottom line is I go about 1/16" greater OD than I need to be sure I have room to clean it up for a nice finish.
 
Great thanks for the replies and I'm new at this. I have a Emco Maximat V10-P. My greatest concern is for a nice finished look.How is cold rolled steel for working with? I want to use it to get some practice in with as it's cheap to buy.
 
Selection depends on two things not relative to the material itself. Where you are located and availability. Now for the size itself. It would probably be easier to find .125 over rather ihan .062 over. When I buy I usually go for +.125.

"Billy G"
 
Yes Bill availability is the problem. I live out in the boon docks and there is no small lot supplier unless I make a 50 mile trip. So I'm limited to TSC and Fastenal for metal at the moment. I'm sure once I start turning more material making a trip to a proper supplier will be worth while. But for now I'm restricted to whats available locally. For now I'll most likely be going with material that is 1/6 over size so I can get a nice finish.
 
Wheresmywrench? said:
Great thanks for the replies and I'm new at this. I have a Emco Maximat V10-P. My greatest concern is for a nice finished look.How is cold rolled steel for working with? I want to use it to get some practice in with as it's cheap to buy.
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Stock diameter depends upon the intended function of your part and on your equipment. In some cases, The as received stock O.D. is sufficient; surface finish is acceptable and roundness and concentricity are not an issue. For instance, if I were making a 1/2" long spacer , 1/4" I.D. , 1/2" O.D. to offset a plate, the concentricity of the the I.D to O.D., the O.D. finish, and the actual O.D. are not critical so I would just use 1/2" rod and drill the 1/4" hole and cut to length. If I were making a press fit bushing to serve as a bearing for a shaft, O.D., roundness, and surface finish are critical so I would select a stock diameter that would permit me to clean up the O.D.

Things to consider when selecting stock: 1. stock is seldom truly round 2. stock is seldom truly straight, 3. lathe chucks seldom have zero runout 4. actual stock diameters are often different than nominal.
If you are buying stock from a vendor like McMaster Carr, MSC, or Enco, they give tolerances for the nominal diameter. If you are buying from a local DIY, take along your calipers if the diameter is critical.

One final thought. I, as well as many others, I'm sure, am guilty of designing things with nice round numbers for dimensions which can mean that I have to go to the next larger size stock. If you have the freedom to pick your dimensions, it would be wise to design with slightly smaller dimensions than available stock sizes
 
It also depends on how round or exact you need something. Some of the stock I've used needs turned down quite a bit before it is even round. If it is pitted you my run out of material before you get the pits out.

Taking a skim cut on scale is hard on the tool & hard to get the correct size on. I like to be able to take .020" on my first cut.
 
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